We will study how the primary somatosensory cortex processes information about the texture, shape, and softness of objects. Evoked responses in single neurons in the postcentral gyrus (SI: areas 1, 2, and 3) will be recorded electrophysiologically in the behaving monkey during tactile stimulation of the fingerpads of the contralateral hand. Transparent objects-surfaces that differ in shape (single curvatures or curvature patterns that vary in curvature radius), texture (micro-gratings of different heights and spacings), or compliance (rubber surfaces differing in softness) will be applied to the skin in two ways: (1) Passive Touch. The surfaces will be pressed against the skin (in studies of softness or curvature) or pressed and stroked across the skin (in studies of texture or curvature) of the restrained hand with precise control over compressional force and displacements along two axis. Monkeys will either attend to the stimuli by making tactile discriminations or not attend by performing and irrelevant visual tracking task. (2) Active Touch. Monkeys will discriminate tactually by actively palpating the object surfaces in prescribed ways that provide some experimental control over and measurement of the forces applied against the object and the trajectory and velocity of the fingertip movement. We will test the hypothesis that (a) cortical responses to surfaces of objects (curvature, texture, compliance) are modulated, not only by specific proprioceptive and/or tactile input, but also by appropriate movements of the hand and by selective attention during sensory performance; (b) there is a hierarchical processing of object surface information, i.e., a rostrocaudal gradient in complexity of neuronal response. Thus, new information will be obtained on how cortical neurons process information about texture, shape, and softness of object surfaces in SI of awake behaving monkeys.
